In addition to the hydrorefining state-of-the-art practiced in the presence of a hydrorefining catalyst, hydrogen and high temperatures and pressures, other techniques have been disclosed for the removal of these nitrogen compounds. Recently, two U.S. patents issued to Baset, U.S. Pat. Nos. 4,332,676 and 4,332,675 which disclose a process for the removal of basic nitrogen compounds from organic streams inclusive of petroleum oils utilizing gaseous sulfur dioxide to thereby precipitate a salt comprising the basic nitrogen compound, sulphur dioxide and water with downstream separation of the precipitated salt. Both of these patents concern a single phase treatment system with the content of water in the separation system in '675 being substantially eliminated and the quantity of water in '676 being such that only a single phase system is existent. In fact, in the latter reference the addition of water is limited to a concentration only to the extent that a two-phase liquid system will never be formed. It is also disclosed that a non-polar solvent can be utilized in the contacting step such as a petroleum ether, a lower paraffinic hydrocarbon or an aromatic hydrocarbon such as toluene. While the types of basic organic nitrogen compounds extracted in the instant invention are either similar to or the same as those described at Column 2 of the '676 disclosure, the means by which the process is undertaken in the instant invention is very different from that disclosure.
In the October 1983 issue of Chemical Engineering by Desai and Madgavkar, cognizance is taken of a method to remove catalyst-poisoning nitrogen compounds from shale oil by solvent extraction with a formic acid/water solvent prior to hydrotreating. The advantage of this technique is a lowering of the hydrogen consumption and a reduction of the nitrogen content to a tolerable level feasible for downstream processing of the shale oil. It should be noted that the nitrogen compounds indigenous to the shale oil are unique and will not necessarily behave in the same manner as the nitrogen compounds indigenous to the petroleum oils. Further, shale oil liquids are derived from a polymeric material "kerogen", which is thermally decomposed into liquids which contain the nitrogen molecules. Petroleum oils are formed by biological and chemical action by nature over a much longer period of time, are more mature than shale-derived oils and have a chemical constituency far different from shale-derived oils. Also, the starting materials in formulation of the petroleum oil versus the shale oil are very different and lead to a lower content of nitrogen compounds for the petroleum oil than the shale oil. The method of nitrogen extraction in re the latter can simply not be extrapolated to the former.
In addition of inorganic acids to petroleum oils to reduce the quantity of nitrogen compounds has long been established. For example, in U.S. Pat. No. 2,352,236 anhydrous hydrogen chloride is added to improve a charge stock for catalytic cracking. A dilute acid, such as sulfuric acid, is disclosed in U.S. Pat. No. 1,686,136 to complex nitrogen compounds existent in a California-derived crude oil. The organic carboxylic acids, sometimes referred to as low molecular weight fatty acids of high volatility, have been used to complex nitrogen-bases in such disclosures as U.S. Pat. Nos. 2,263,175 and 2,263,176. While these latter two references employ a portion of the chemical mechanism utilized in the second step of this two-step nitrogen extraction process, they fail to disclose, suggest or even hint at the use of a first step to concentrate the nitrogen compounds to more effectively utilize the treating and excising step with the lower aliphatic carboxylic acids. Also, these references fail to teach the use of a combination carboxylic acid system such as an admixture of formic and acetic acid, which is important in light of the cross production of an acetic acid, i.e. formic acid will usually be present as an impurity. Thus, it may be economic and advantageous to use a mixture of such co-produced carboxylic acids.